| The Physicochemical properties, molecular structure, galetinization mechanism, retrogradation mechanism of rice starch and their fractions from indica rice, japonica rice and glutinous rice were studied by laser light scattering, differential scanning calorimeter, x-diffraction, and gel permeation chromatography. Results indicated:1. Fractions and molecular structure of rice starchRice starch has 2~3 main fractions, among them, indica rice has 3 fractions of amylose (Am), intermatial fraction (Im) and amylopectin (Ap). The average-weight molecule of indica Am is 0.44x10 g/mol, Ap is 47.15x106g/mol. Japonica rice has 3 fractions of amylose (Am), intermatial fraction (Im) and amylopectin (Ap). The average-weight molecule of japonica Am is 1.62x106g/mol, Ap is 66.10x105g/mol. Glutinous rice has 2 fractions of intermatial fraction (Im) and amylopectin (Ap). The average-weight molecule of glutinous Ap is 234.90x106g/mol.There are 5-6 degrees branched chains in a Ap molecule, which with 4~6 chains in a main chain(C chain) and 1~2 chains in every branch chain respectively. Glutinous rice has higher branched degree and shorter branch chains.Am displayed the semi-rigid single helix structure in dilute DMSO solution. The conformation of Ap is related to molecular weight, branched degree and external chain length. Ap from Glutinous rice that with greater molecular weight and branched degree, shorter external chain length displayed rigid sphere with curly external chain in DMSO solution, displayed flexible sphere with coil structure in litter higher concentration of DMSO-aqueous solution. The Ap from indica rice and japonica rice that with lower molecular weight and branched degree, longer external chain displayed the shape of more rigid star in DMSO solution.2. Physicochemical properties and gelatinization mechanism of starchStarches from indica rice, japonica rice and glutinous rice have the similar polyhedron shape. The components of the three kinds of rice are similar except amyloes content. Among the three kinds of rice, indica rice has the lowest amylopectin content, crystal melt energy, gel consistent and intrinsic viscosities. While, glutinous rice with the highest amylopectin content, crystal melts energy, gel consistent and intrinsic viscosities.Gelatinization mechanism of native starch under excessive water was suggested: swelling of starch granule, melt of crystal, divorce of Am from starch granule, and formed continuous phase of Am coil solution and disperse phase of Ap conglomeration. Nature of gelatinization is the melt of starch crystal, and gelatinization lead to the dispart of starch fractions (Am and Ap).Gelatinization mechanism of native starch under limited water is suggested: limited swelling of starch granule, melt of crystal, divorced of Am from starch granule and surround Ap granule, formed flow region of Am and elasticity region of Ap conglomeration. Nature of gelatinization is the melt of starch crystal, and formed the stick-elasticity body with two "micro-region".3. Retrogradation mechanism of starchRetrogradation mechanism of starch paste (with excessive water) is suggested that the Ap conglomeration agglomerated, the coil network developed, Am and Ap interact each other, rigidity of starch molecule increase with storage time. Retrogadation result of the increase of sedimentation, and lead to the phase dispart.Retrogradation mechanism of starch gel (with limited water) is suggested that Ap in elasticity region and Am in flow region retrogradation in the region of themselves respectively, Am and outer chain of Ap recrystal, coil network of Am in flow region development, rigidity of starch molecule increase. Am and Ap interact each other and weakened retrogradation.4. Processing and retrogradation of rice foodAccording to the food quality and starch properties, indica rice is suitable to produce rice-flour noodles, which is required to have the smooth, tenacity mouthfeeling. Japonica rice is suitable to produce instant rice, which is required t...
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